Osteosarcoma Overview

Overview

Osteosarcoma is the most common type of cancer of the bone. It is the third most common malignancy in children and adolescents, accounting for approximately 5% of all cancers in these age groups. In children and adolescents, 50% of osteosarcomas arise from the bones around the knee. The cause of most cases of osteosarcoma is unknown although a genetic predisposition is suspected. The main known cause of osteosarcoma is radiation therapy. Osteosarcoma is a relatively frequent complication in survivors of childhood cancers treated with radiation therapy with a latency period of 15-20 years.1,2

Osteosarcoma originates most frequently in the thigh bone (distal femur), lower leg (proximal tibia) or upper arm (proximal humerus). Symptoms of osteosarcoma depend on the extent of disease, but may include pain, swelling, localized enlargement of the extremity and, occasionally, a bone fracture without trauma. At the time of diagnosis, approximately 80% of patients have localized osteosarcoma and the remainder have metastatic osteosarcoma.

Diagnostic Procedures

It is imperative that patients with diagnosed or suspected osteosarcoma undergo an evaluation by an orthopedic oncologist who is familiar with surgical management of this disease. Patients should undergo this evaluation prior to an initial biopsy, since an inappropriately performed biopsy may jeopardize a subsequent limb-sparing procedure.

There are several methods for diagnosing osteosarcoma. At this time, controversy exists over which of these methods is optimal.

Open Incisional Biopsy: An open incisional biopsy involves a wide incision through the skin in order to expose the suspicious mass so that a tissue sample can be removed and analyzed in a laboratory. Complications occur in approximately 16% of patients that receive this type of biopsy. In some cases, these complications could lead to unnecessary amputation.

Percutaneous Biopsy: A percutaneous biopsy, is an effective method for making a diagnosis before surgery. Since most patients are currently treated with neoadjuvant chemotherapy, it is important to make the diagnosis prior to surgery. A percutaneous core needle biopsy is a procedure in which a small needle with a hollow core is placed into the suspicious mass and a tissue sample is collected. This procedure uses computed tomography (CT) or fluoroscopy to help guide the biopsy needle.3 In a recent study of 110 primary bone tumors, a percutaneous biopsy resulted in accurate diagnosis in all but 13 cases.

Fine Needle Aspiration Biopsy (FNAB): FNAB is another type of biopsy in which a very fine needle is placed into the mass for the collection of a cell sample, and is less invasive than the percutaneous biopsy. However, an adequate number of cells are difficult to obtain through FNAB, often times resulting in the need for a patient to undergo a repeat biopsy. One study using FNAB resulted in a conclusive diagnosis in only 65% of 40 patients.4

Other: Additional tests may help determine the extent or stage of osteosarcoma. X-ray examinations commonly detect bone destruction and increased bone formation caused by osteosarcoma. Computed tomography (CT) scans and bone scans using isotopes are recommended as part of the staging process to detect lung and bone metastases, respectively.

Staging

The process of identifying the extent of the cancer is called staging. Accurately identifying the stage of a cancer helps determine what treatment will be most effective. Staging is particularly important for determining whether a cancer has spread from its original site to other parts of the body. Although there are more sophisticated staging systems for patients with osteosarcoma, it is most convenient to categorize the cancer as localized, metastatic, and recurrent.

Localized Osteosarcoma Localized cancers are limited to the bone of origin. In these cases, smaller tumors that are separate from the primary cancer, called “local skip metastases”, may be apparent within the bone, indicating a worse prognosis. Approximately 50% of primary osteosarcomas occur in the upper leg. Of these, 80% arise adjacent to the knee joint in young patients. Other primary sites are the lower leg, upper arm, pelvis, jaw, and ribs.

Metastatic Osteosarcoma Metastatic osteosarcoma has spread beyond the primary site of origin. Metastatic disease is diagnosed when staging tests reveal evidence of disease in the lung, other bones, or other distant sites. More than 80% of patients with metastatic osteosarcoma have cancer that has spread to the lung. The second most common site of spread is another bone.

Recurrent Osteosarcoma Patients with recurrent osteosarcoma have disease that has recurred after a complete response or have disease that was not eradicated with initial treatment. The most common sites for recurrent osteosarcoma are the lungs and bone.